Trigger circuits



July 27, 1965 N. A. JUKES TRIGGER CIRCUITS Filed 001;. l, 1962 United States Patent 3,197,649 TRIGGER (IIRCUITS Norman Alfred .Iulres, Walsail, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England Filed Oct. 1, 1962, Ser. No. 227,224 Claims priority, application Great Britain, Oct. 6, 1961, 35,980/61 1 Claim. (Cl. 301-83) This invention relates to trigger circuits for producing an output pulse of current when the voltage across a coil reaches a predetermined level.

A trigger circuit in accordance with the invention comprises in combination first and second input terminals adapted for connection to a source of direct or rectified alternating current, first and second output terminals, a square loop core, a first winding on said core having its ends connected to the output terminals respectively, a second winding on the core having one end connected to the second input terminal through said coil and its other end connected to the second input terminal through a first diode, a third winding on the core having one end connected to the first input terminal and its other end connected through a first resistor to the collector terminal of a transistor, the base terminal of which is connected to said other end of the second winding, a second diode bridging the ends of the third winding, a second resistor connecting the emitter terminal of the transistor to the first input terminal, and a third resistor and a capacitor connected in parallel between the emitter terminal of the transistor and the second input terminal, the arrangement being such that when the voltage acros said coil reaches a predetermined level the transistor will be rendered conductive and an output pulse will appear at the output terminals, whereafter no further output pulses can be obtained until the core is driven to its original state.

The accompanying drawing is a circuit diagram illustrating one example of the invention.

Referring to the drawing, there are provided first and second input terminals 1, 2 adapted for connection to a source of direct or rectified alternating current so as to be of negative and positive polarity in use. There is further provided a ferrite or other magnetic core 3 having a substantially square wave hysteresis loop, and on this core are wound first, second and third windings 4, 5, 6.

The winding 4 has its ends connected to a pair of out put terminals 7, 8 respectively, whilst one end of the winding is connected to the terminal through a coil 9 across which a voltage is to be applied. The other end of the winding 5 is connected to the terminal 2. through a diode 1h.

The winding 6 is bridged by a diode 11, and has one end connected to the terminal. Its opposite end is coning 5. The emitter of the transistor 3 is connected to the terminal 1 through a resistor 14, and to the terminal 2 through a resistor 15 and a capacitor 16 in parallel.

The arrangement is such that normally the core is in its negative remanent state and the transistor is held in its non-conductive state by the resistors 14, 15. However, if an increasing voltage is generated in the coil 9 the transistor 3 is biased in a manner to permit it to conduct. As soon as the transistor 3 conducts, current flows in the winding 6 and induces a voltage in the windings 4, 5. The voltage induced in the winding 5 renders the transistor more conductive, and this re-generative action continues until the core 3 changes to its positive remanent state, at which point a large output pulse is received by the output terminals 7, 8. The transistor is protected by the diode 11. Thereafter, no further output pulse can be received until the core 3 is re-set by generating a reverse voltage in the coil 9, such a voltage being applied by way of the diode 10 to the winding 5.

The trigger circuit described can be used in a variety or" applications where an output pulse is required and an alternating voltage is generated in the coil.

Having thus described my invention what I claim as new and desire to ecure by Letters Patent is:

A trigger circuit for producing an output pulse of current when the voltage across a coil reaches a predetermined level comprising in combination with said coil first and second input terminals adapted for connection to a source of direct or rectified alternating current, first and second output terminals, a square loop core, a first winding on said core having its ends connected to the output terminals respectively, a second winding on the core having one end connected to the second input terminal through said coil and its other end connected to the second input terminal through a first diode, a third winding on the core having one end connected to the first input terminal and its other end connected through a first resistor to the collector terminal of a transistor, the base terminal of which is connected to said other end of the second winding, a second diode bridging the ends of the third winding, a second resistor connecting the emitter terminal of the transistor to the first input terminal, and a third resistor and a capacitor connected in parallel between the emitter terminal of the transistor and the second input terminal, the arrangement being such that when the voltage across said coil reaches a predetermined level the transistor will be rendered conductive and an output pulse will appear at the output terminal, whereafter no further output pulses can be obtained until the core is driven to its original state.

References Cited by the Examiner UNITED STATES PATENTS 3,015,736 1/62 Schultz et al 340-174 X IRVING L. SRAGOW, Primary Examiner. 

